1. Field of the Invention
The present invention relates to a mass and heat transfer device and method. More particularly it is a heat and mass transfer device formed as a capillary fluted tube especially effective in evaporation and desorption devices such as found in heat transfer machines.
2. Background
Absorption refrigeration machines are heat operated refrigeration machines that operate on one of the earliest know principles of refrigeration. In its basic form, it consists of an interconnected absorber, desorber (generator), condenser, and evaporator that use a refrigerant and an absorbent as a refrigerant or solution pair and a heat source to transfer heat between a heat load and a heat sink.
The absorber contacts low pressure refrigerant vapor with a miscible absorbent. Absorption takes place as a result of the mixing tendency of the miscible materials as well as an affinity between the refrigerant vapor and the absorbent and results in the generation of thermal energy which is released to the heat sink. The mixture formed by the absorption process, which is referred to here as a strong solution, is typically pressurized by means of a solution pump and conveyed via a heat exchanger to the desorber (generator).
The generator (desorber) causes the refrigerant vapor and absorbent to separate as a result of the application of heat. When the absorbent is a nonvolatile material, heating of the strong solution is sufficient to accomplish complete separation of the refrigerant vapor. The remaining absorbent, referred to as a weak solution, is returned to the absorber to again begin the absorption process.
When the absorbent is a volatile material such as water in an ammonia/water refrigerant pair, a rectifier is required to move the last traces of the volatile absorbent (water) from the refrigerant vapor (ammonia). As used here, the term "rectifier" includes all types of fractional distillation equipment used to remove a volatile absorbent from the refrigerant vapor. Rectification results in heat generation as the volatile absorbent condenses to a liquid. The heat from the rectification process is also released to a heat sink. Removal of the absorbent from the refrigerant vapor is essential in that contamination of the refrigerant vapor with absorbent interferes with refrigerant vaporization in the latter refrigerant vaporization step.
After rectification, the vapor passes to the condenser. The condenser condenses the refrigerant vapor to a liquid with the liberation of heat. The hot liquid refrigerant then passes to the evaporator.
The evaporator revaporizes the hot refrigerant liquid at low pressure and temperature with input of heat from the heat load, i.e., from the refrigerator, room, building, or other medium the system was designed to cool. From the evaporator, the refrigerant vapor enters the absorber to again cycle through the process. FIG. 24 illustrates a typical single cycle absorption system. The temperature of the components increases from left to right while pressure increases from bottom to top.
In its basic form, the generator typically is a vertical tank in which strong solution is heated. The strong solution can be heated by means of a heat exchange coil that is submerged in the strong solution and through which is passed either steam or a hot liquid. Alternatively the generator may be heated by hot gases such as the combustion products from the combustion of a fuel source such as natural gas. To facilitate heat transfer when using combustion products, the vertical tank is typically finned on the outside to extract heat from the combustion products.
U.S. Pat. No. 4,972,692 (Re. 34,747) Petty et al. discloses a generator made from a finned double-wound helical coil of tubing. The tubing is a conventional, single tube with small, fine fins. Hot combustion products are circulated through the fins of the coils of the generator with a blower. A second generator is formed from a fluted tube within a conventional tube, that is, so called fluted tube-in-tube construction. The fluted tube-in-tube is formed as a helical winding. Hot weak solution from the first generator is used to heat an intermediate solution to desorb refrigerant from the intermediate solution. The intermediate solution flows within the interior of the fluted tube while the hot, weak solution from the first generator flows between the interior of the conventional outer tube and the exterior of the inner fluted tube. Other than this effort, no other attempts have been made to explore the use of coiled helical fluted tubes to improve the desorption process.
Although some effort has been made in the use of fluted and capillary tubes in other arts, these do not suggest the current invention. For example, U.S. Pat. No. 4,438,807 Mathur et al. discloses a heat transfer tube having an internal helical rib to create fluid turbulence within the tube and an external fin that is selectively bent to form passages and openings for reentrant nucleate boiling. The tube is typically used as an evaporator with refrigerant fluid flowing on the outside of the tube. Heat transfer takes place from the fluid flowing within the tube. U.S. Pat. No. 4,589,481 Masson shows a tube heat exchanger having twisted and flattened tubes that are arranged into bundles of tubes having essentially straight and parallel lines. The tubes are arranged with four adjacent tube center lines forming a square or three adjacent tube center lines forming a triangle. The twisted ribs and valleys of the tubes can be aligned so that the distance between tube centers is less than the sum of the radii of the circles that circumscribe the tubes. The degree of flattening can also vary from one end of the tube to the other and a group of tubes may have both left and right screw orientations in the same tube set. U.S. Pat. No. 5,219,021 Edelstein et al. describes an improved design for a heat pipe capillary channel in which the working fluid layer thickness is minimized to afford a large surface area with good, thin film heat transfer. The capillary channels are axially grooved along the length of the tube and provide good evaporation and condensation when used as a heat pipe.
U.S. Pat. No. 5,325,684 Stierlin et al. discloses an absorber than has four spaced-apart concentric windings of oval tubes through which a cooling fluid flows. The concentric coils are arranged in a closed annular cylinder. A divided, weak solution pours over the outside of the oval tubes from the top of the cylinder to form a thin film. A helical space exists between the coil windings that allows for redistribution of weak solution on the coil surfaces as it flows downward. The outer surfaces of the tubes are knurled or have spiralled grooves to enhance good wetting of the tube surfaces. U.S. Pat. No. 3,730,229 D'Onofrio discloses a heat exchanger using helically corrugated tubes. As is apparent, other than the work of Petty et al., little, if anything, has been done to improve mass and heat transfer efficiencies thorough the use of twisted fluted tubes.
Accordingly, it is an object of the present invention to provide an improved twisted fluted tube that better effects a more efficient heat and mass transfer process occurring within the twisted tube.
Another object of this invention is to provide improved liquid-vapor equilibrium conditions within the twisted fluted tube.
Another object of this invention is to improve the heat transfer efficiency on the exterior surface of the twisted fluted tube.
Another object of this invention is to provide a heat and mass transfer device that can be used with a wide variety of heat transfer fluids.
Another object of this invention is to provide a device for the effective direct heat transfer between endothermic and exothermic processes.
Another object of this invention is to provide system components that are simple and easy to manufacture.
Another object of this invention is to provide for improved twisted fluted tube devices that can be more effectively connected to each other.
Another object of this invention is to provide an improved twisted fluted tube configuration for use with evaporation, desorption, absorption, condensation, and rectification processes.
Another object of this invention is to provide improved twisted fluted tubes for use in heat transfer absorption machines.
Other objects of the invention will become more apparent to those with ordinary skill in the art from consideration of the present disclosure.